Chlamydial eye disease has probably been endemic in Egypt and other ancient civilizations for centuries.¹⁷ Chlamydia trachomatis, transmitted by flies, fingers, and fomites, is prevalent where access to water is limited and facial cleanliness is poor. Trachoma belts used to extend around the world, and areas of hyperendemic trachoma still persist (Fig. 43.2). Trachoma affects over 300 million people, especially women and children living in deprived communities of Africa, Asia, Australia, the Middle East, and South America.¹⁸ Familial clustering may arise from shared exposures or genetic susceptibility.¹⁹ Trachoma may affect the majority of children in a hyperendemic area (Table 43.5), where 10% to 30% of children are reinfected each year.²⁰ Nearly 6 million people with trachoma have low vision from residual corneal scarring. Trachomatous visual impairment accounts for an annual loss of 2 million disability-adjusted life-years, and results in lost economic productivity of $3 billion per year.^21,22

Onchocerciasis is an insect-borne infection endemic in rural parts of Africa and Latin America. People living near streams and watercourses where blackfly vectors breed are at risk of being infected, especially if they engage in river-bank activities such as fishing, farming, and washing. The endemicity of onchocerciasis in equatorial Africa is measured in decades during which infection and blindness lead to a cycle of human migration. Tribes settle in fertile valleys, remain until the level of river blindness reaches an unsustainable level, and then abandon villages to move to the hills. Later, the tribes relocate back to the rivers after several generations, thus continuing a pattern that may have gone on for centuries.²³ Environmental and climatic changes play a role in the spread of onchocerciasis, although different strains of Onchocerca volvulus transmitted by different Simulium vectors may contribute to the prevalence and spectrum of ocular findings in diverse locales.²⁴ Two million people have onchocercal visual loss. Onchocerciasis forfeits 500,000 disability-adjusted life-years each year and can consume 5% of an endemic country’s gross national product because of stagnant agricultural output.²⁵

Mycobacterium leprae infection follows contact with an infected individual or other source after an incubation period of about 3 years. An intemperate fear of contagion contributes to segregation and psychosocial stigma of people with Hansen disease. Still persisting in poor, crowded regions, its distribution is nonhomogenous, troubling some families more than others. Ocular disease affects about 10% of people with Hansen disease. Multibacillary leprosy occurs in Southeast Asia and South America and produces chronic uveitis. Paucibacillary leprosy predominates on the Indian subcontinent and in Africa, and is associated with exposure keratopathy and neurotrophic keratopathy. About 5% of leprosy patients are blind, totalling 250,000 people, largely from secondary cataract or corneal opacification.²⁶

Ophthalmia neonatorum is conjunctivitis affecting infants younger than 1 month. In the mid-18th century, transmission via the infected birth canal was first suspected when it was recognized that the risk of ophthalmia neonatorum tripled if the mother had vaginal secretions.²⁷ Before Credé introduced silver nitrate eye drops in the late 19th century, approximately 10% to 15% of newborns developed bacterial conjunctivitis. Up to a half of children in schools for the blind during the 19th century had corneal scarring from ophthalmia neonatorum.²⁸

The current incidence varies by the availability of obstetric care (Table 43.6). Annual rates of gonococcal and chlamydial conjunctivitis per 1,000 live births are approximately 0.3 and 5, respectively, in the United States but are ten times greater in parts of Africa. The epidemiology of neonatal conjunctivitis corresponds to fluctuations in maternal sexually transmitted disease (Fig. 43.3). Each case of neonatal conjunctivitis represents a cluster of family members and associates with sexually transmitted disease.²⁹ The risk of corneal complications from ophthalmia neonatorum is higher among the poor. Between 1,000 and 4,000 infants are blinded each year.²⁸

Fifty million eye injuries take place each year.³⁰ In some regions, over 1% of the population sustains a corneal abrasion or wound.³¹ Although less than 5% of traumatized eyes become infected,³¹ globally two million new cases of trauma-related microbial keratitis occur annually.¹³ Compared to North America and Europe, agrarian regions have 10 times the incidence of posttraumatic microbial keratitis, where the poor are at greatest risk.^32,33,34 Common bacterial causes include Streptococcus pneumoniae and Staphylococcus aureus, whereas agricultural accidents predispose to filamentous fungi such as Fusarium and Aspergillus species.³⁵ The use of traditional medications may delay medical treatment or lead to secondary infection (36,37).^36,37 Trauma with ensuing microbial keratitis accounts for 5% of blinding conditions and 50% of unilateral blindness.^13,38